David W. Brook, M.D., and his American colleagues studied whether drug use in childhood, adolescence and early adulthood could predict development of psychiatric disorders late in the third decade of life.

According to background information in the article, previous studies have linked legal and illegal drug use and psychological disorders. Drug use has also been strongly correlated with substance use disorders including nicotine dependence, anxiety, and affective disturbances.

The researchers examined data from a community-based sample of 736 adults who had been interviewed with use of age-appropriate versions of the University of Michigan Composite International Diagnostic Interview at the mean ages of 14, 16, 22 and 27 years. Presence or absence of psychiatric disorders and drug use were recorded at each interview.

The researchers found that tobacco use in adolescents and young adults was significantly associated with an increased risk of alcohol dependence and substance abuse disorders at a mean age of 27 years. However, it was not associated with new episodes of major depressive disorder. Earlier use of alcohol, marijuana, and other illegal drugs significantly predicted later major depressive disorder, alcohol dependence, and substance abuse disorders by the age of the last interview.

The authors also found that except for the effect of tobacco use on major depressive disorder, early drug use was significantly related to later psychiatric disorders even after controlling for age, sex, parental education level, family income, and prior episodes of major depressive disorder and substance use disorders.

"As predicted, our results demonstrate that the cumulative frequency of drug use (alcohol, marijuana, and other illegal drugs) covering the period of childhood and early adolescence, middle and late adolescence and/or early adulthood was associated with episodes of major depressive disorder, alcohol dependence, and substance use disorders in the late 20s," the authors wrote.

"The study provides evidence that drug use precedes major depressive disorder and alcohol dependence and is not merely a consequence of these disorders. Related to this, the study demonstrates that certain types of drug use (namely, marijuana) during childhood and adolescence should not necessarily be treated as benign conditions that the youth may outgrow. ... unlike other studies, our data demonstrate that the relationship between drug use and psychiatric disorders can hold across a large span of time (roughly 14 years)," added the researchers.